1. Field of the Invention
The present invention relates to the field of multichannel audio reproduction systems and, more particularly, to a system for producing tri-ambient synthesized audio signals from a stereo source.
2. The Prior Art
The art is replete with systems designed to reproduce faithfully music recordings and other audio sounds. The most familiar of these systems involves the use of stereo signals, namely, simultaneously recording two separate signals and subsequently reproducing these signals through separate speakers. Generally, the signals correspond to left and right channels which have been derived from microphones positioned to the left and right of a recording stage, for example.
In an effort to improve on the two-speaker stereo arrangement, it has also been known to provide additional speakers driven by the left and right stereo channels. For example, enhanced reproduction can be achieved by providing speakers at the rear of a listening room to complement stereo speakers situated at the front of the room. In this manner, the area within the room at which the stereo signals coincide is effectively enlarged, leading to increased utilization of the room's listening area.
In the systems discussed above, the signals delivered to the speakers are generally maintained in phase with each other. That is, in response to a particular signal appearing on all channels, all of the speaker cones are driven in unison in identical directions. It is also known in the art, however, to provide systems utilizing signals which are out-of-phase with each other. Examples of such prior art devices are disclosed in U.S. Pat. Nos. 3,757,047 and 3,697,692.
One manner in which such out-of-phase signals can be derived is to provide signals resulting from various combinations of the left and right channel stereo signals. Further, the effect of such out-of-phase signals may be enhanced by delivering these signals to speakers arranged in predetermined configurations about a listener. In U.S. Pat. No. 3,745,254, for example, a reproduction system is disclosed in which four speakers spaced equidistantly apart relative a listener are provided with left (L), right (R), left minus right (L-R), and right minus left (R-L) signals, respectively.
According to this patent, however, superior reproduction is not achieved unless a phase shift is also introduced between the two difference signals. In order to introduce such a phase shift, it is necessary to utilize a variety of active electrical circuits, adding considerably to the cost of such a system. Furthermore, the presence of these additional components increases the likelihood of a breakdown occurring in the field, which breakdown may even affect other components in the system.